Nanotechnology Spotlight – Latest Articles

Shorter-wavelength surface-emitting laser sources are important for a variety of fields including photonics, information processing and biology. Researchers in Japan were successful in developing a current-driven blue-violet photonic crystal surface-emitting laser. They developed a fabrication method, named 'air holes retained over growth', in order to construct a two-dimensional gallium nitride/air photonic crystal structure. The resulting periodic structure has a photonic crystal band-edge effect sufficient for the successful operation of a current-injection surface-emitting laser. This represents an important step in the development of laser sources - from both a scientific and engineering point of view - that could be focused to a size much less than the wavelength and be integrated two-dimensionally at such short wavelengths.

DNA, the blueprint of life, and electronics seem to be two completely different things but it appears that DNA could offer a solution to many of the hurdles that need to be overcome in further scaling down electronic circuits beyond a certain point. The reason why DNA could be useful in nanotechnology for the design of electric circuits is the fact that it actually is the best nanowire in existence - it self-assembles, it self-replicates and it can adopt various states and conformations. Not surprisingly, performing reliable experiments on a single oligo-DNA molecule is an extremely delicate task as partly contradicting research reports demonstrate: Different DNA transport experiments have shown that DNA may be insulating, semiconducting, or metallic. Among the numerous factors that could impact the results are the quality of the DNA-electrode interface, the base pair, the charge injection into the molecule, or environmental effects such as humidity or temperature. Researchers have now demonstrated a novel carbon nanotube-based nanoelectronic platform as proof of concept that single DNA molecules can be detected. This novel detection technique is based on change in electrical conductance upon selective hybridization of the complementary target DNA with the single stranded probe attached to the system. The single-stranded sequence-specific probe DNA whose ends are modified with amine is attached between two carbon nanotubes/nanowires using dielectrophoresis (DEP). This platform can be used for understanding how electrical charge moves through DNA which could help researchers understand and perhaps develop a technique for reversing the damage of DNA done by oxidation and mutation.

One of the more interesting concerns of nanotechnology is 'grey goo.' The term was invented by Eric Drexler to describe one of the dangerous issues that must be faced as nanotechnology capabilities evolve. Here's how it works. 1. Pretend that nanotechnology truly exists to the point where we can fabricate machines of arbitrary complexity using individual atoms or molecules. 2. Pretend that these machines have sufficient complexity and computational means that they can make copies of themselves using whatever happens to be lying within their reach. 3. Pretend that their fabrication systems are such that they can make a copy of themselves about once an hour. 4. Pretend that one of these machines decides to do nothing except make copies of itself.

In 1954, Richard Buckminster Fuller was granted U.S. Pat. No. 2,682,235 for geodesic domes, a method of enclosing space in architectural applications. The geodesic dome combines the structural advantages of the sphere (which encloses the most space within the least surface, and is strongest against internal pressure) with those of the tetrahedron (which encloses least space with most surface and has the greatest stiffness against external pressure). Subsequently, soccer ball shaped carbon molecules known as fullerenes or buckyballs were named for their resemblance to a geodesic sphere. But is not only certain carbon molecules where Nature uses sphere-like forms. Spheres can be found at all scales in both the inanimate and living world for the basic physical property of encapsulation. Spherical virus capsids (a capsid is the protein shell of a virus), for example, enclose space by using the geometry of the icosahedron, thus exploiting the economy of this form in terms of both surface area-to-volume ratio and genetic efficiency of subunit-based symmetric assembly. Many viruses' capsids use icosahedral symmetry to form particles ranging from 20 to 200 nanometers in size. Researchers have now begun to copy Nature's icosahedral-symmetry design principles for molecular containers, which could solve the problem of designing and synthesizing stable molecular containers having very large interior.

Looking at Nature as a successful design lab with millions of years of research experience, it is quite surprising that scientists haven't tried harder to copy some of Nature's more successful and impressive design blueprint. The list of actual commercialized biodesign-inspired products is very short. The most famous is Velcro, the hook-loop fastener that was invented in 1945 by Swiss engineer, George de Mestral. The idea came to him after he took a close look at the burrs (seeds) of burdock which kept sticking to his clothes and his dog's fur on their daily summer walks in the Alps. He examined their condition and saw the possibility of binding two materials reversibly in a simple fashion. And then, of course, there are the Wright Brothers, who modeled their planes on the structure of bird wings. Today, there are quite a number of terms such as bionics, biomimetics, biognosis, biomimicry, or even 'bionical creativity engineering' that refer to more or less the same thing: the application of methods and systems found in Nature to the study and design of engineering systems and modern technology. The use of design concepts adapted from Nature is a promising new route to the development of advanced materials and increasingly nanotechnology researchers find nanostructures a useful inspiration for overcoming their design and fabrication challenges. Because biological structures are the result of hundreds of thousands of years of evolution, their designs possess many unique merits that would be difficult to achieve by a complete artificial simulation. However, utilizing them as biotemplates and converting them to inorganic material could be a highly reproducible and low-cost process for fabricating complex nanostructures with unique functions. Complex functional systems are still out of reach but the replication of biological structures is making good progress. A recent example is the fabrication of antireflection nanostructures by replicating fly eyes.

Even the smartest scientists can still learn from the dumbest animals - at least as far as materials science is concerned. Take for instance marine glass sponges such as the hexactinellid sponge Euplectella sp. which are considered to be one of the most primitive animals in existence. Nevertheless, they produce integrated composite materials with outstanding mechanical properties and researchers are interested in finding out how they do that and how this natural process could be copied and adapted for use in the fabrication of synthetic composite materials. Euplectella's bioglass filaments, for instance, exhibit a rather complex design, thus ensuring the control of both mechanical and chemical interfaces between the different components to overcome the brittleness of the main constituent material, glass. Scientists have found that the amazing properties of many biological high-performance materials such as bone or shells are a result of the structure and the interplay of the constituents. In other words, the hierarchical structure of composites determines their material properties, and not the type of the composite's constituents. Researchers in Germany have now reported a biomimetic approach for the fast fabrication of hierarchically structured peptide-silica fibers, mimicking the bio-silicification process of natural glass fibers.

As a critical component of optoelectronic devices, transparent conductive coatings pervade modern technology. The most widely used standard coating is indium tin oxide (ITO), used in nearly all flat panel displays and microdisplays. Causing problems for manufacturers, though, Indium is expensive and scarce and demand is increasing. From the depressed levels of $60/kg in 2002, indium prices rose to over $1,000/kg during the summer of this year. Recently, prices have fallen back to between $400-$500/kg. But, geologists say the cost of indium may not matter soon, because the earth's supply of this element could be gone within just a few years. In addition to the limited availability of Indium there are other reasons that make ITO and other metal oxides such as FTO (fluorine tin oxide) increasingly problematic for electronics manufacturers: the instability of these metal oxides in the presence of acid or base; their susceptibility to ion diffusion into polymer layers; their limited transparency in the near-infrared region; and lastly, the current leakage of FTO devices caused by FTO structure defects. This has made the search for novel transparent electrode materials with good stability, high transparency and excellent conductivity a crucial goal for optoelectronic researchers. Recent work by researchers in Germany exploits ultra-thin transparent conductive graphene films as window electrodes in solar cells.

As an emerging science, nanotoxicology is expanding the boundaries of traditional toxicology from a testing and auxiliary science to a new discipline where toxicological knowledge of nanomaterials can be put to constructive use in therapeutics as well as the development of new and better biocompatible materials. Until now, though, no one has been able to pin-point which properties determines or influences the inherent hazards of nanoparticles. Now, scientists have developed a framework that can be applied to a suggested hazard identification approach and is aimed at identifying causality between inherent physical and chemical properties and observed adverse effects reported in the literature.